Rotatable member with an annular groove for dynamic balancing during rotation

ABSTRACT

A method is provided for balancing a rotating member having an annular balancing groove which is configured to receive and retain a balancing projectile. The method includes determining a circumaxial imbalance location, and firing a balancing projectile in timed relationship with the rotation of the member so that the balancing projectile enters the groove at the imbalance location. Such steps are repeated as required to cure additional points of imbalance.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. patent application Ser. No.10/754,284 filed on Jan. 9, 2004 now U.S. Pat. No. 7,305,905 andentitled “A ROTATABLE MEMBER WITH AN ANNULAR GROOVE FOR DYNAMICBALANCING DURING ROTATION”, the content of which is herein incorporatedin its entirety.

BACKGROUND OF THE INVENTION

Manual dynamic balancing of rotatable members is still common practicewith the member being rotated to determine the points of unbalance, therotation stopped to attach weights manually, and the member perhapsrotated a second time to check the balance. Obviously, this is a tediousand time-consuming procedure. Attempts at automation have not beenwidely successful.

U.S. Pat. No. 2,432,659 to Criswell first determines the locationsrequiring added weight and then sprays “small particles of metal”repeatedly until the member is balanced.

U.S. Pat. No. 2,937,613 discloses firing a “Body” at a groove in arotating member but does not disclose any means for capturing andretaining the “Body”.

U.S. Pat. No. 3,968,769 to Gusarov et al. projects glue onto thecircumaxial locations requiring balancing.

U.S. Pat. No. 5,992,232 to Saitoh ejects a liquid balancing agent, whichrequires curing.

Patent application Ser. No. 10/788,106 (now U.S. Pat. No. 7,231,822)entitled Machine and Method for Balancing a Member During Rotation, thecontent at which is hereby incorporated by reference, discloses a systemsimilar to the foregoing patents but which fires projectiles of metal orthe like at a rotating member for balancing the same. The system ishighly efficient but requires a means of capturing the projectiles andpositively retaining the same at the desired circumaxial locations.

The foregoing patents are hereby incorporated herein by reference.

It is the general object of the present invention to provide projectilecapturing and retaining means on a rotating member in a simple andefficient manner.

SUMMARY OF THE INVENTION

In fulfillment of the foregoing object and in accordance with thepresent invention, an annular groove is provided in a member to bebalanced and has a cross sectional configuration slightly smaller thanthat of the projectile at least after impact in at least one directionof measurement so as to engage and capture the projectile for retentionin the groove. The groove may retain the projectile frictionally or,preferably, the projectile may be retained by positive engagement of thegroove wall therewith. This condition may result from a groove designwherein the mouth of the groove is narrower than the interior with atleast one mouth-defining portion of the groove wall being flexible forentry of the projectile to the interior of the groove. Preferably, theside of the mouth opposite the flexible portion is inclined from theline of flight of the projectile in the range of 10-55 degrees wherebyto direct errant projectiles into the groove, and more specificallyapproximately 30 degrees. Once the projectile has entered the groove,the flexible portion of the groove wall engages and positively clampsthe same therein. Alternatively, positive retention of a projectile in agroove may be provided for with a relatively soft projectile, whichexpands on impact within a groove so as to become larger than the mouthof the groove.

Once captured in a groove it is of course important that unintended oraccidental circumaxial movement of the projectiles along the groove bepositively prevented. To meet this need, small transverse ribs areprovided in a spaced circumaxial series and one or more ribs may bepartially deformed on impact whereby to provide the necessary retentionof the projectiles at the specific locations required for balancing therotatable member.

Examples of rotatable members which can be advantageously balanced withthe aid of a balancing groove of the invention are air impellers andsmall electric motors. Centrifugal air impellers and small permanentmagnet D.C. motors are specifically discussed herein below.

Finally, a method of balancing employing projectiles fired at rotatingmembers is also discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the drawings illustrates a centrifugal air impeller partiallyin section provided with a pair of balancing grooves in accordance withthe invention.

FIG. 2 is an enlarged fragmentary top view partially in section of abalancing groove.

FIG. 3 is an enlarged cross sectional view of a balancing groove with aprojectile in flight and about to enter the groove.

FIG. 4 is an enlarged fragmentary longitudinal section of a grooveshowing a plurality of transverse ribs engaging and retaining aprojectile against movement along the groove.

FIG. 5 is an enlarged fragmentary cross sectional view of a groove andprojectile of an alternative embodiment of the invention.

FIG. 6 is a view of still another embodiment of the invention.

FIG. 7 is a view in partial cross section of a small electric motorprovided with a pair of balancing grooves.

FIG. 8 is a fragmentary perspective view of a centrifugal air impellerhaving a specific blade, end ring and back plate construction and whichis provided with balancing grooves in its end ring and back plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring particularly to FIG. 1, it will be observed that a centrifugalair impeller indicated generally at 10 is provided with a pair ofannular balancing grooves 12 and 14 respectively in end ring 16 and backplate 18. Parallel circumaxially spaced longitudinally extending airmoving blades 20, 20 interconnect the end ring 16 and the back plate 18.The grooves 12 and 14 may be identical in construction and are bestillustrated in FIGS. 2 and 3.

Referring particularly to FIG. 3 it will be observed that the mouth ofthe groove 14 at A is somewhat narrower than the interior. A left handwall portion or lip 22 would tend to block entry of a projectile largerthan A but is flexible so as to bend leftwardly sufficiently to allowthe projectile to pass and assume the broken line position in theinterior of the groove as shown. In the broken line position theprojectile is engaged by the lip as it returns to its normal positionand a clamping force is exerted by the lip on the projectile urging itagainst the opposite wall of the groove. Thus, the projectile iscaptured and positively retained in the groove.

Still referring to FIG. 3, the wall portion 21 of the groove oppositethe lip 22 is shown inclined toward the interior of the groove at anangle α with the line of flight of the projectile. The purpose of thisinclined portion is to direct errant projectiles into the groove and theangle of inclination from the projectile line of flight should fall inthe range of 10 to 55 degrees. Preferably the angle should beapproximately 30 degrees. It should also be noted that the lip 22 has ashallow arcuate surface 26 facing inwardly so as to be engaged byprojectiles causing the lip to flex outwardly and opening the mouth forprojectile entry.

Further in accordance with the present invention, anti-rotation ribs 28,28 are provided to retain projectiles in the groove against accidentalor inadvertent movement along the groove. As best illustrated in FIGS. 3and 4, a plurality of ribs 28, 28 are provided in circumaxially spacedrelationship along the base of each groove. A projectile such as 24 inFIG. 4 may partially crush a single rib as shown or it may rest betweentwo ribs perhaps partially crushing each. In either event the projectileis restrained against movement along the groove.

In the embodiment of the invention thus far described, the air impellerand thus the balancing groove are of molded plastic construction and theprojectile is of metallic construction, the latter actually taking theform of a conventional BB of the type fired from a child's toy rifle.Alternatively, both elements may be of metallic construction or, as willbe seen, a relatively soft material may be employed for the projectileand a somewhat harder material for the groove wall.

FIG. 5 illustrates an alternative embodiment of the invention wherein arelatively soft material such as plastic or lead is used for theprojectile 24 a and a somewhat harder material such as steel is used forthe groove walls 30. The projectile in this instance should be slightlysmaller than the mouth A of the groove 14 a. Thus, the projectile freelyenters the groove and on impact with the rear wall of the groove deformsslightly so as to flatten somewhat and engage the side walls of thegroove which are inclined to make the rear of the groove wider that itsmouth. As will be apparent, the projectile is thus captured andpositively held in the groove at the desired location. A series of smallribs 32, 32 may be provided as above to retain the projectile inposition circumaxially.

A further alternative embodiment of the invention is shown in FIG. 6. Agroove 14 b has walls 34, 34 which incline inwardly from the mouth ofthe groove to engage a projectile with progressively greater force as itproceeds into the groove. This of course results in a substantialfrictional retaining force against withdrawal of the projectile fro thegroove. To enhance this retaining force small longitudinally extendingribs 36, 36 may be provided on the sidewalls 34, 34. The ribs may beslightly deformed by the projectile to provide a hybrid frictional andpositive retention of the projectile.

A further application of balancing grooves is illustrated in FIG. 7.Small electric motor 40 which may be of the permanent magnet DC type,has an external rotor 42 and a stator 44. Depending on the axialdimension of the rotor, one or two balancing grooves may be required. Asshown, two grooves 46, 48 are provided at opposite sides of the rotorand face in opposite directions. The grooves 46, 48 may be identical andthey may also be identical with the above-described grooves 12 and 14 onthe air impeller of FIG. 1.

FIG. 8 illustrates the application of balancing grooves to a specificdesign of a centrifugal air impeller fully disclosed in U.S. patentapplication Ser. No. 10/700,308, entitled “INJECTION MOLDED CENTRIFUGALAIR IMPELLER” filed Oct. 31, 2003, hereby incorporated herein byreference. The impeller design emphasizes the provision of a moldparting line at an intermediate longitudinal portion of blades 45, 45 asshown by the broken line 46. Balancing grooves 49, 50 are providedrespectively at end ring 52 and back plate 54 and may be identical withthe grooves of FIG. 1. The end ring 52 is considerably enlarged relativeto the end ring of the aforementioned patent application to accommodatethe balancing groove 49.

Finally, the general method of balancing a rotating member as set forthin the aforementioned patent applications incorporated herein byreference is greatly enhanced by the addition of a balancing groove.Thus, an improved method in accordance with the invention comprisesproviding an annular balancing groove in a member requiring balancing,determining a location where a balancing weight is needed, firing aprojectile in timed relationship with the rotation of the member so thatthe projectile enters the groove at the predetermined location, andrepeating the foregoing steps as required to cure additional points ofimbalance.

1. A method for balancing a rotating member comprising the steps ofproviding an annular balancing groove in the member which is configuredto receive and retain a balancing projectile, said annular balancinggroove having a mouth portion that is narrower than an interior portionof said annular balancing groove, and at least one mouth-defining wallportion being flexible for entry of the projectile into the interior ofthe groove; determining a circumaxial imbalance location, firing abalancing projectile in timed relationship with the rotation of themember so that the balancing projectile enters the groove at saidimbalance location; repeating the foregoing steps as required to cureadditional points of imbalance.
 2. A method for balancing a rotatingmember as set forth in claim 1 wherein a flexible lip is provided at oneside of the mouth of the groove and the groove is so configured anddimensioned that the lip engages the projectile after entry and exerts aclamping force to positively retain the projectile in the groove.
 3. Amethod for balancing a member during rotation comprising the steps ofproviding a means for securing in position one or more balancingprojectiles fired at the member, determining balancing weight andlocation required for balancing the member, including determining thebalancing positions of two or more projectiles which will balance themember where a single balancing projectile exhibits a projectile weightunequal to said balancing weight, at least one of said positions beingspaced circumaxially from the point of imbalance, and firing two or moreprojectiles at the positions which will balance the member while saidmember is rotating.
 4. A method for balancing a member during rotationas set forth in claim 3 wherein the balancing weight required to balancethe member is determined to be less than that of said projectile weight.